The Clinical Significance of Maximum Tumor Diameter on MRI in Men Undergoing Radical Prostatectomy or Definitive Radiotherapy for Locoregional Prostate Cancer

• Published in: International journal of radiation oncology, biology, physics Vol. 111; no. 3; pp. e277 - e278
• Main Authors: Hutten, R., Parsons, M.W., Khouri, A., Tward, A., Wilson, T., Peterson, J., Morrell, G., Kokeny, K.E., Lloyd, S., Cannon, D.M., Tward, J.D., Sanchez, A., Johnson, S.B.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-11-2021
• ISSN: 0360-3016; 1879-355X
• DOI: 10.1016/j.ijrobp.2021.07.895

Given recent results of the FLAME trial evaluating tumor boost using radiotherapy (RT), the impact of maximum tumor diameter (MTD) of the dominant prostate cancer (PCa) nodule on prostate cancer outcomes requires further investigation. MTD from radical prostatectomy (RP) pathologic specimens and pretreatment MRI have both been identified as a potential biomarker for adverse outcomes. We aim to evaluate the impact of pretreatment MRI derived MTD on progression-free survival (PFS) after definitive intent treatment with RP or RT.
Patients receiving RP or RT for PCa with available pretreatment MRI were identified retrospectively from an institutional database. Radiographic MTD was extracted from pretreatment MRI reports. Progression free survival was defined as freedom from biochemical failure, metastasis, or additional cancer-directed therapy following definitive treatment. RT and surgical cohorts were analyzed separately. Multivariable cox proportional hazards models for progression were created from clinical variables including NCCN risk group, presence of ECE or SVI on MRI, MTD, and use of androgen deprivation therapy. Significant covariates were used in a classification and regression tree (CART) analysis with a significance level of P < 0.05 in order to identify prognostic groups. PFS was estimated with the Kaplan-Meier method.
Of 631 patients, 428 (67.8%) received surgery and 203 (32.2%) received RT. The RT cohort included 36 (13.8%) low dose rate brachytherapy alone (LDR), 106 (40.6%) external beam radiotherapy alone (EBRT), and 119 (45.6%) combined LDR+EBRT patients. The study population included NCCN low-risk (LR, 8.1%), intermediate-risk (IR, 60.3%), and high-risk (HR, 31.5%) patients with an overall median follow up of 2.7 years (inter-quartile range: 1.5-4.3). NCCN risk group and MTD were independently associated with progression in both cohorts. CART analysis for the surgical cohort identified 3 prognostic groups: NCCN low/intermediate risk with MTD < = 14mm (Relative Hazard Ratio [RHR] = 0.12; 3y PFS 97.6%, 95% confidence interval [92.5-99.2%]), NCCN low/intermediate risk with MTD > = 15mm (RHR = 1.06, 3y PFS 78.1%, [68.7-85.0%]), and NCCN high risk (RHR = 2.60, 3y PFS 52.6%, [41.5-62.6%]). CART analysis for the RT cohort identified 2 prognostic groups: MTD < = 22mm (RHR = 0.69, 3y PFS 93.3%, [87.8-96.3%]) and MTD > = 23mm (RHR = 2.58, 3y PFS 84.1% [65.7-93.1%]).
MTD appears to be an independent prognostic factor for progression in NCCN LR/IR patients undergoing RP and all patients undergoing RT regardless of NCCN risk grouping. Notably, our analysis reveals different prognostic MTD cut points depending on the treatment modality, with LR/IR patients undergoing surgery having inferior PFS if MTD > = 15mm and those undergoing RT having inferior PFS if MTD > = 23mm. Further investigation of MTD as a biomarker for selecting patients that may benefit from treatment escalation is warranted.